The Exilarch exercised both civil and judicial functions, and all the Jews of Babylonia formed a separate community under him. Bostanaï also obtained the exceptional permission to wear a signet-ring (Gushpanka). By this means he was able to give his documents and decrees an official character. The seal, in reference to some unknown historical allusion, bore the impress of a fly. Bostanaï must have been an important personage in other respects, since legends cluster about him, and would make his birth itself appear a miraculous event. The Judæo-Babylonian community, which had acquired some importance through Bostanaï, obtained its real strength under Ali, the fourth Caliph, Mahomet's comrade and son-in-law, the hero of Chaibar.
Omar had died at the hands of an assassin (644), and his successor, Othman, had been killed in an insurrection (655). Ali was nominated Caliph by the conspirators, but he had to struggle against many bitter opponents. Islam was divided into two camps. The one declared for Ali, who resided in the newly-built town of Kufa; the other for Moawiyah, a relative of the murdered Caliph Othman.
The Babylonian Jews and Nestorian Christians sided with Ali, and rendered him assistance. A Jew, Abdallah Ibn-Sabâ, was a spirited partisan of Ali. He asserted that the succession to the Caliphate was his by right, and that the divine spirit of Mahomet had passed to him, as it had from Moses to Joshua. It is said that when Ali took the town of Firuz-Shabur or Anbar, 90,000 Jews, under Mar-Isaac, the head of a college, assembled to do homage to the Caliph, who was but indifferently supported by his own followers (658). The unhappy Ali valued this homage, and, doubtless, accorded privileges to the Jewish principal. It is quite probable that from this time the head of the school of Sora was invested with a certain dignity, and took the title of Gaon. There were certain privileges connected with the Gaonate, upon which even the Exilarch did not venture to encroach. Thus a peculiar relation, leading to subsequent quarrels, grew up between the rival offices – the Exilarchate and the Gaonate. With Bostanaï and Mar-Isaac, the Jewish officials recognized by the Caliph, there begins a new period in Jewish history – the Epoch of the Geonim. After Bostanaï's death dissension arose among his sons. Bostanaï had left several sons by various wives, one of them the daughter of the Persian king. Perhaps her son was his father's favorite, because royal blood flowed in his veins, and he was probably destined to be his successor. His brothers by the Jewish wives were consequently jealous of him, and treated him as a slave, i. e., as one that had been born of a captive non-Jewess, who, according to Talmudic law, was looked upon as a slave, so long as he could not furnish proof that either his mother or himself had been formally emancipated. This, however, he could not do. The brothers then determined to sell the favorite, their own brother, as a slave. Revolting as this proceeding was, it was approved by several members of the college of Pumbeditha, partly from religious scruples, partly from the desire to render a friendly service to Bostanaï's legitimate sons. Other authorities, however, maintained that Bostanaï, who was a pious man, would not have married the king's daughter before he had legally freed her, and made her a proselyte. In order to protect her son from humiliation, one of the chief judges, Chaninaï, hastened to execute a document attesting her emancipation, and thus the wicked design of the brothers was frustrated; but the stain of illegitimacy still attached to the son, and his descendants were never admitted to the rank of the descendants of the Exilarch Bostanaï.
Bostanaï's descendants in the Exilarchate arbitrarily deposed the presidents of the colleges, and appointed their own partisans to the vacant places. The religious leaders of the people thus bore Bostanaï's descendants a grudge. Even in later times, an authority amongst the Jews had to defend himself with the words: "I am a member of the house of the Exilarch, but not a descendant of the sons of Bostanaï, who were proud and oppressive." The vehement quarrels about the Caliphate, between the house of Ali and the Ommiyyades, were repeated on a small scale in Jewish Babylonia. The half-century from Bostonaï and the rise of the Gaonate till the Exilarchate of Chasdaï (670 to 730) is in consequence involved in obscurity. Few also of the Geonim who held office and of the presidents of the colleges during this period are known, and their chronological order cannot be ascertained. After Mar-Isaac, probably the first Gaon of Sora, Hunaï held office, contemporaneously with Mar-Raba in Pumbeditha (670 to 680). These presidents issued an important decree with respect to the law of divorce, whereby a Talmudical law was set aside. According to the Talmud, the wife can seek a divorce only in very rare cases, e. g., if the husband suffers from an incurable disease. Even if the wife were seized with an unconquerable aversion to her husband, she could be compelled by law to live with him, and to fulfil her duties, on penalty of losing her marriage settlement, and even her dowry, in case she insisted upon the separation. Through the domination of Islam circumstances were now changed. The Koran had somewhat raised the position of women, and empowered the wife to sue for a divorce. This led many unhappy wives to appeal to the Mahometan courts, and they compelled their husbands to give them a divorce without the aforesaid penalties. It was in consequence of the events just related that Hunaï and Mar-Raba introduced a complete reform of the divorce laws. They entirely abrogated the Talmudical law, and empowered the wife to sue for a divorce without suffering any loss of her property-rights. Thus the law established equality between husband and wife. For the space of forty years (680 to 720), only the names of the Geonim and Exilarchs are known to us; historical details, however, are entirely wanting. During this time, as a result of quarrels and concessions, there arose peculiar relations of the officials of the Jewish-Persian kingdom towards one another, which developed into a kind of constitution.
The Jewish community in Babylonia (Persia), which had the appearance of a state, had a peculiar constitution. The Exilarch and the Gaon were of equal rank. The Exilarch's office was political. He represented Babylonian-Persian Judaism under the Caliphs. He collected the taxes from the various communities, and paid them into the treasury. The Exilarchs, both in bearing and mode of life, were princes. They drove about in a state carriage; they had outriders and a kind of body-guard, and received princely homage.
The religious unity of Judaism, on the other hand, was embodied in the Gaonate of Sora and Pumbeditha. The Geonim expounded the Talmud, with a view to a practical application of its provisions; they made new laws and regulations; administered them, and meted out punishment to those that transgressed them. The Exilarch shared the judicial power with the Gaon of Sora and the head of the college of Pumbeditha.
The Exilarch had the right of nomination to offices, though not without the acquiescence of the college. The head of the college of Sora, however, was alone privileged to be styled "Gaon"; the head of the college of Pumbeditha did not bear the title officially. The Gaon of Sora together with his college, as a rule, was paid greater deference than his colleague of Pumbeditha, partly out of respect to the memory of its great founders, Rab and Ashi, partly on account of its proximity to Kufa, the capital of Irak and of the kingdom of Islam in the East. On festive occasions, the head of the college of Sora sat at the right side of the Exilarch. He obtained two-thirds of certain revenues for his school, and performed the duties of the Exilarch when the office was vacant. For a long time, too, only a member of the school of Sora was elected president of the school of Pumbeditha, this school not being permitted to elect one from its own ranks.
Now that the Exilarch everywhere met with the respect due a prince, he was installed with a degree of ceremony and pomp. Although the office was hereditary in the house of Bostanaï, the acquiescence of both colleges was required for the nomination of a new Exilarch, and thus there came to be a fixed installation service. The officials of both the colleges, together with their fellow-collegians, and the most respected men in the land, betook themselves to the residence of the designated Exilarch. In a large open place, which was lavishly adorned, seats were erected for him and the presidents of the two schools. The Gaon of Sora delivered an address to the future Exilarch, in which he was reminded of the duties of his high office, and was warned against haughty conduct toward his brethren. The installation always took place in the synagogue, and on a Thursday. Both officials put their hands upon the head of the nominee, and declared amidst the clang of trumpets,